nav, aside, main {
    position: absolute;
}

nav {
    top: 0;
    left: 180px;
    right: 0;
    height: 50px;
}

aside {
    top: 0;
    left: 0;
    bottom: 0;
    width: 180px;
}

main {
    top: 50px;
    left: 180px;
    right: 0;
    bottom: 0;
}
